The invention relates to the field of motor vehicle navigation systems, and in particular to a navigation system that receives supplemental navigation data over a wireless communication channel.
Motor vehicle navigation systems are growing in popularity due to their ability to direct the driver along a route between a starting point and a destination. For example, published German patent application DE 197 34 365 A1 discloses a mobile radio receiver for use in a motor vehicle, which is combined with a navigation unit. The radio receiver includes user interfaces and a multimedia unit, which includes a digital radio receiving unit and a backward channel unit. The navigation unit consists of a navigation processor and a memory unit. A position location unit, a sensor unit, and a communication unit are connected to the navigation unit. The user interfaces are connected to the multimedia unit and are controlled by a control unit.
In the arrangement described in German patent application DE 197 34 365 A1, the data needed for information and traffic directions are transmitted together with the digital radio signals. Interactive services are initiated and controlled by the user through a backward channel (i.e., the system is used interactively).
The memory unit stores only basic data, such as for example throughways, state routes, interstate routes, and all place names. With this data the navigation processor can calculate the directions to the destination using roads of higher order. Low order data necessary for navigation, such as street names, highways of lower order, and urban streets, are transmitted to the navigation processor from a central station.
In a first embodiment, DE 197 34 365 A1 discloses that the navigation processor requests the other data necessary for navigation from a service provider, via the communication unit or via the backward channel unit implemented in the digital radio broadcast. The control unit filters the transmitted navigation data out of the radio broadcast signal and provides this received navigation data to the navigation processor.
In a second embodiment, DE 197 34 365 A1 discloses that the other data needed for navigation (e.g., street names, highways of lower order, urban streets, etc.) are broadcast continuously in addition to and together with the digital radio signal. In cooperation with the digital radio receiving unit and the control unit, the navigation processor detects from the continuously transmitted data stream the data needed for navigation.
Both of these embodiments suffer from the problem that the data needed for navigation must be retrievable at all times. Therefore, if the receiving unit breaks down or if the service provider is unable to provide the requested data, directions to the destination are then possible only on the basis of higher order streets.
Therefore, there is a need for a navigation system that includes a sufficiently updated database to provide improved availability of route search and destination directions.